1. Field of the Invention
The present invention relates to a process for converting ethers to alcohols, and particularly to a process for the aquathermolysis of ethers in an aqueous environment.
2. Description of Related Art
Various processes are described in the prior art for the conversion of ethers into a mixture comprising predominantly alcohols and olefins.
Generally speaking, ethers are less commercially valuable than the corresponding alcohol and olefin reaction products which may be produced by cleavage of the ether. This is particularly important from the economic standpoint when such ethers are formed as an undesirable by-product in chemical reactions. For example, aliphatic alcohols are commercially manufactured by hydrating the appropriate monoolefin in the presence of an acid catalyst. The reaction product usually contains minor quantities of the corresponding alkyl ether as a low-value by-product. More specifically, the hydration of propylene with sulfuric acid generally yields a reaction mixture comprising isopropyl alcohol and up to about 20% by weight of isopropyl ether as a by-product. Also, during the commercial manufacture of methyl ethyl ketone by the hydration of n-butene to sec-butyl alcohol, followed by oxidation of the alcohol over a fixed bed catalyst, substantial quantities of sec-butyl ether are generated which is also a low-value product.
Prior art processes for the conversion of ethers into alcohols generally involve cleavage of the ether in an aqueous or non-aqueous medium and in the presence of an acidic catalyst.
For example, U.S. Pat. No. 2,045,785 discloses the conversion of ethers such as ethyl ether to alcohols such as ethanol by a process wherein the ether is converted using a dilute aqueous solution of an acid catalyst by subjecting the mixture to temperatures within the range of 200.degree. to 300.degree. C. and pressures of from about 225 to 3000 psig. for a period of from about 10 to 60 minutes. Preferred acids are stronger acids such as sulfuric, phosphoric or hydrochloric, but weaker acids such as acetic are also disclosed, and the acid concentration in the aqueous medium ranges from 5 to 20%. Salts which are acidic in aqueous medium may also be employed as catalysts.
It is to be noted in Examples 1-3 that where HCl is the catalyst, the amount of ethylene obtained in addition to ethanol is a function of the time of the reaction and the temperature of the reaction.
U.S. Pat. No. 2,519,061 discloses a process for cleaving ethers to form alcohols by passing an aqueous mixture of the ether over a catalyst comprising metal oxides at temperatures within the range of 350.degree. to 800.degree. F. and pressures from atmospheric up to 200 atmospheres.
U.S. Pat. No. 4,357,147 discloses a process for producing an oxygenated fuel blending stock by hydration and oligomerization of propylene, wherein the isopropyl ether by-product is converted to propylene, isopropyl alcohol, and water in a reversion zone using alumina or a zeolite as the catalyst. U.S. Pat. No. 4,405,822 teaches a related process for producing alcohols by olefin hydration, wherein the ether by-product is converted using a large molar excess of water in the presence of an acid ion exchange resin.
U.S. Pat. No. 4,751,343 teaches the preparation of tertiary olefins with simultaneous production of alcohols by cleavage of tertiary alkyl ethers when mixed with water over strong acid cation exchangers. U.S. Pat. No. 4,804,704 describes cross-linked acidic resins suitable for use in cleaving tertiary ethers. EP-302,336 teaches tertiary ether cleavage using a column apparatus containing an acidic ion exchange resin and employing a stream of deionized water.
U.S. Pat. No. 4,395,580 teaches the production of tertiary olefins by decomposing tertiary ethers with steam over an alumina catalyst containing Ti, Zr and/or Hf.
U.S. Pat. No. 4,581,475 teaches the direct conversion of aliphatic ethers to aliphatic alcohols by reacting the ether with an excess of water at high temperature and at a pressure sufficient to keep the reactants in the liquid phase and in the presence of a strong acid ion exchanger.
While these and similar processes are generally effective and efficient insofar as they go, they all suffer from the requirement that catalysts are used in the processes. In commercial processes, the presence of significant levels of acidic catalyst materials in the production of liquids and gases gives rise to corrosive problems with respect to production equipment and additional production expense with respect to the disposition of acidic effluents in an environmentally acceptable manner. The utilization of "bed" catalysts such as zeolites or acidified polymeric materials requires frequent catalyst regeneration or replacement which diminishes the economy of the process.